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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  linux/fs/locks.c
  *
  * We implement four types of file locks: BSD locks, posix locks, open
  * file description locks, and leases.  For details about BSD locks,
  * see the flock(2) man page; for details about the other three, see
  * fcntl(2).
  *
  *
  * Locking conflicts and dependencies:
  * If multiple threads attempt to lock the same byte (or flock the same file)
  * only one can be granted the lock, and other must wait their turn.
  * The first lock has been "applied" or "granted", the others are "waiting"
  * and are "blocked" by the "applied" lock..
  *
  * Waiting and applied locks are all kept in trees whose properties are:
  *
  *  - the root of a tree may be an applied or waiting lock.
  *  - every other node in the tree is a waiting lock that
  *    conflicts with every ancestor of that node.
  *
  * Every such tree begins life as a waiting singleton which obviously
  * satisfies the above properties.
  *
  * The only ways we modify trees preserve these properties:
  *
  *  1. We may add a new leaf node, but only after first verifying that it
  *     conflicts with all of its ancestors.
  *  2. We may remove the root of a tree, creating a new singleton
  *     tree from the root and N new trees rooted in the immediate
  *     children.
  *  3. If the root of a tree is not currently an applied lock, we may
  *     apply it (if possible).
  *  4. We may upgrade the root of the tree (either extend its range,
  *     or upgrade its entire range from read to write).
  *
  * When an applied lock is modified in a way that reduces or downgrades any
  * part of its range, we remove all its children (2 above).  This particularly
  * happens when a lock is unlocked.
  *
  * For each of those child trees we "wake up" the thread which is
  * waiting for the lock so it can continue handling as follows: if the
  * root of the tree applies, we do so (3).  If it doesn't, it must
  * conflict with some applied lock.  We remove (wake up) all of its children
  * (2), and add it is a new leaf to the tree rooted in the applied
  * lock (1).  We then repeat the process recursively with those
  * children.
  *
  */
 
 #include <linux/capability.h>
 #include <linux/file.h>
 #include <linux/fdtable.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/security.h>
 #include <linux/slab.h>
 #include <linux/syscalls.h>
 #include <linux/time.h>
 #include <linux/rcupdate.h>
 #include <linux/pid_namespace.h>
 #include <linux/hashtable.h>
 #include <linux/percpu.h>
 #include <linux/sysctl.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/filelock.h>
 
 #include <linux/uaccess.h>
 
 #define IS_POSIX(fl)    (fl->fl_flags & FL_POSIX)
 #define IS_FLOCK(fl)    (fl->fl_flags & FL_FLOCK)
 #define IS_LEASE(fl)    (fl->fl_flags & (FL_LEASE|FL_DELEG|FL_LAYOUT))
 #define IS_OFDLCK(fl)   (fl->fl_flags & FL_OFDLCK)
 #define IS_REMOTELCK(fl)    (fl->fl_pid <= 0)
 
 static bool lease_breaking(struct file_lock *fl)
 {
     return fl->fl_flags & (FL_UNLOCK_PENDING | FL_DOWNGRADE_PENDING);
 }
 
 static int target_leasetype(struct file_lock *fl)
 {
     if (fl->fl_flags & FL_UNLOCK_PENDING)
         return F_UNLCK;
     if (fl->fl_flags & FL_DOWNGRADE_PENDING)
         return F_RDLCK;
     return fl->fl_type;
 }
 
 static int leases_enable = 1;
 static int lease_break_time = 45;
 
 #ifdef CONFIG_SYSCTL
 static struct ctl_table locks_sysctls[] = {
     {
         .procname   = "leases-enable",
         .data       = &leases_enable,
         .maxlen     = sizeof(int),
         .mode       = 0644,
         .proc_handler   = proc_dointvec,
     },
 #ifdef CONFIG_MMU
     {
         .procname   = "lease-break-time",
         .data       = &lease_break_time,
         .maxlen     = sizeof(int),
         .mode       = 0644,
         .proc_handler   = proc_dointvec,
     },
 #endif /* CONFIG_MMU */
     {}
 };
 
 static int __init init_fs_locks_sysctls(void)
 {
     register_sysctl_init("fs", locks_sysctls);
     return 0;
 }
 early_initcall(init_fs_locks_sysctls);
 #endif /* CONFIG_SYSCTL */
 
 /*
  * The global file_lock_list is only used for displaying /proc/locks, so we
  * keep a list on each CPU, with each list protected by its own spinlock.
  * Global serialization is done using file_rwsem.
  *
  * Note that alterations to the list also require that the relevant flc_lock is
  * held.
  */
 struct file_lock_list_struct {
     spinlock_t      lock;
     struct hlist_head   hlist;
 };
 static DEFINE_PER_CPU(struct file_lock_list_struct, file_lock_list);
 DEFINE_STATIC_PERCPU_RWSEM(file_rwsem);
 
 
 /*
  * The blocked_hash is used to find POSIX lock loops for deadlock detection.
  * It is protected by blocked_lock_lock.
  *
  * We hash locks by lockowner in order to optimize searching for the lock a
  * particular lockowner is waiting on.
  *
  * FIXME: make this value scale via some heuristic? We generally will want more
  * buckets when we have more lockowners holding locks, but that's a little
  * difficult to determine without knowing what the workload will look like.
  */
 #define BLOCKED_HASH_BITS   7
 static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);
 
 /*
  * This lock protects the blocked_hash. Generally, if you're accessing it, you
  * want to be holding this lock.
  *
  * In addition, it also protects the fl->fl_blocked_requests list, and the
  * fl->fl_blocker pointer for file_lock structures that are acting as lock
  * requests (in contrast to those that are acting as records of acquired locks).
  *
  * Note that when we acquire this lock in order to change the above fields,
  * we often hold the flc_lock as well. In certain cases, when reading the fields
  * protected by this lock, we can skip acquiring it iff we already hold the
  * flc_lock.
  */
 static DEFINE_SPINLOCK(blocked_lock_lock);
 
 static struct kmem_cache *flctx_cache __read_mostly;
 static struct kmem_cache *filelock_cache __read_mostly;
 
 static struct file_lock_context *
 locks_get_lock_context(struct inode *inode, int type)
 {
     struct file_lock_context *ctx;
 
     /* paired with cmpxchg() below */
     ctx = smp_load_acquire(&inode->i_flctx);
     if (likely(ctx) || type == F_UNLCK)
         goto out;
 
     ctx = kmem_cache_alloc(flctx_cache, GFP_KERNEL);
     if (!ctx)
         goto out;
 
     spin_lock_init(&ctx->flc_lock);
     INIT_LIST_HEAD(&ctx->flc_flock);
     INIT_LIST_HEAD(&ctx->flc_posix);
     INIT_LIST_HEAD(&ctx->flc_lease);
 
     /*
      * Assign the pointer if it's not already assigned. If it is, then
      * free the context we just allocated.
      */
     if (cmpxchg(&inode->i_flctx, NULL, ctx)) {
         kmem_cache_free(flctx_cache, ctx);
         ctx = smp_load_acquire(&inode->i_flctx);
     }
 out:
     trace_locks_get_lock_context(inode, type, ctx);
     return ctx;
 }
 
 static void
 locks_dump_ctx_list(struct list_head *list, char *list_type)
 {
     struct file_lock *fl;
 
     list_for_each_entry(fl, list, fl_list) {
         pr_warn("%s: fl_owner=%p fl_flags=0x%x fl_type=0x%x fl_pid=%u\n", list_type, fl->fl_owner, fl->fl_flags, fl->fl_type, fl->fl_pid);
     }
 }
 
 static void
 locks_check_ctx_lists(struct inode *inode)
 {
     struct file_lock_context *ctx = inode->i_flctx;
 
     if (unlikely(!list_empty(&ctx->flc_flock) ||
              !list_empty(&ctx->flc_posix) ||
              !list_empty(&ctx->flc_lease))) {
         pr_warn("Leaked locks on dev=0x%x:0x%x ino=0x%lx:\n",
             MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev),
             inode->i_ino);
         locks_dump_ctx_list(&ctx->flc_flock, "FLOCK");
         locks_dump_ctx_list(&ctx->flc_posix, "POSIX");
         locks_dump_ctx_list(&ctx->flc_lease, "LEASE");
     }
 }
 
 static void
 locks_check_ctx_file_list(struct file *filp, struct list_head *list,
                 char *list_type)
 {
     struct file_lock *fl;
     struct inode *inode = locks_inode(filp);
 
     list_for_each_entry(fl, list, fl_list)
         if (fl->fl_file == filp)
             pr_warn("Leaked %s lock on dev=0x%x:0x%x ino=0x%lx "
                 " fl_owner=%p fl_flags=0x%x fl_type=0x%x fl_pid=%u\n",
                 list_type, MAJOR(inode->i_sb->s_dev),
                 MINOR(inode->i_sb->s_dev), inode->i_ino,
                 fl->fl_owner, fl->fl_flags, fl->fl_type, fl->fl_pid);
 }
 
 void
 locks_free_lock_context(struct inode *inode)
 {
     struct file_lock_context *ctx = inode->i_flctx;
 
     if (unlikely(ctx)) {
         locks_check_ctx_lists(inode);
         kmem_cache_free(flctx_cache, ctx);
     }
 }
 
 static void locks_init_lock_heads(struct file_lock *fl)
 {
     INIT_HLIST_NODE(&fl->fl_link);
     INIT_LIST_HEAD(&fl->fl_list);
     INIT_LIST_HEAD(&fl->fl_blocked_requests);
     INIT_LIST_HEAD(&fl->fl_blocked_member);
     init_waitqueue_head(&fl->fl_wait);
 }
 
 /* Allocate an empty lock structure. */
 struct file_lock *locks_alloc_lock(void)
 {
     struct file_lock *fl = kmem_cache_zalloc(filelock_cache, GFP_KERNEL);
 
     if (fl)
         locks_init_lock_heads(fl);
 
     return fl;
 }
 EXPORT_SYMBOL_GPL(locks_alloc_lock);
 
 void locks_release_private(struct file_lock *fl)
 {
     BUG_ON(waitqueue_active(&fl->fl_wait));
     BUG_ON(!list_empty(&fl->fl_list));
     BUG_ON(!list_empty(&fl->fl_blocked_requests));
     BUG_ON(!list_empty(&fl->fl_blocked_member));
     BUG_ON(!hlist_unhashed(&fl->fl_link));
 
     if (fl->fl_ops) {
         if (fl->fl_ops->fl_release_private)
             fl->fl_ops->fl_release_private(fl);
         fl->fl_ops = NULL;
     }
 
     if (fl->fl_lmops) {
         if (fl->fl_lmops->lm_put_owner) {
             fl->fl_lmops->lm_put_owner(fl->fl_owner);
             fl->fl_owner = NULL;
         }
         fl->fl_lmops = NULL;
     }
 }
 EXPORT_SYMBOL_GPL(locks_release_private);
 
 /**
  * locks_owner_has_blockers - Check for blocking lock requests
  * @flctx: file lock context
  * @owner: lock owner
  *
  * Return values:
  *   %true: @owner has at least one blocker
  *   %false: @owner has no blockers
  */
 bool locks_owner_has_blockers(struct file_lock_context *flctx,
         fl_owner_t owner)
 {
     struct file_lock *fl;
 
     spin_lock(&flctx->flc_lock);
     list_for_each_entry(fl, &flctx->flc_posix, fl_list) {
         if (fl->fl_owner != owner)
             continue;
         if (!list_empty(&fl->fl_blocked_requests)) {
             spin_unlock(&flctx->flc_lock);
             return true;
         }
     }
     spin_unlock(&flctx->flc_lock);
     return false;
 }
 EXPORT_SYMBOL_GPL(locks_owner_has_blockers);
 
 /* Free a lock which is not in use. */
 void locks_free_lock(struct file_lock *fl)
 {
     locks_release_private(fl);
     kmem_cache_free(filelock_cache, fl);
 }
 EXPORT_SYMBOL(locks_free_lock);
 
 static void
 locks_dispose_list(struct list_head *dispose)
 {
     struct file_lock *fl;
 
     while (!list_empty(dispose)) {
         fl = list_first_entry(dispose, struct file_lock, fl_list);
         list_del_init(&fl->fl_list);
         locks_free_lock(fl);
     }
 }
 
 void locks_init_lock(struct file_lock *fl)
 {
     memset(fl, 0, sizeof(struct file_lock));
     locks_init_lock_heads(fl);
 }
 EXPORT_SYMBOL(locks_init_lock);
 
 /*
  * Initialize a new lock from an existing file_lock structure.
  */
 void locks_copy_conflock(struct file_lock *new, struct file_lock *fl)
 {
     new->fl_owner = fl->fl_owner;
     new->fl_pid = fl->fl_pid;
     new->fl_file = NULL;
     new->fl_flags = fl->fl_flags;
     new->fl_type = fl->fl_type;
     new->fl_start = fl->fl_start;
     new->fl_end = fl->fl_end;
     new->fl_lmops = fl->fl_lmops;
     new->fl_ops = NULL;
 
     if (fl->fl_lmops) {
         if (fl->fl_lmops->lm_get_owner)
             fl->fl_lmops->lm_get_owner(fl->fl_owner);
     }
 }
 EXPORT_SYMBOL(locks_copy_conflock);
 
 void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
 {
     /* "new" must be a freshly-initialized lock */
     WARN_ON_ONCE(new->fl_ops);
 
     locks_copy_conflock(new, fl);
 
     new->fl_file = fl->fl_file;
     new->fl_ops = fl->fl_ops;
 
     if (fl->fl_ops) {
         if (fl->fl_ops->fl_copy_lock)
             fl->fl_ops->fl_copy_lock(new, fl);
     }
 }
 EXPORT_SYMBOL(locks_copy_lock);
 
 static void locks_move_blocks(struct file_lock *new, struct file_lock *fl)
 {
     struct file_lock *f;
 
     /*
      * As ctx->flc_lock is held, new requests cannot be added to
      * ->fl_blocked_requests, so we don't need a lock to check if it
      * is empty.
      */
     if (list_empty(&fl->fl_blocked_requests))
         return;
     spin_lock(&blocked_lock_lock);
     list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests);
     list_for_each_entry(f, &new->fl_blocked_requests, fl_blocked_member)
         f->fl_blocker = new;
     spin_unlock(&blocked_lock_lock);
 }
 
 static inline int flock_translate_cmd(int cmd) {
     switch (cmd) {
     case LOCK_SH:
         return F_RDLCK;
     case LOCK_EX:
         return F_WRLCK;
     case LOCK_UN:
         return F_UNLCK;
     }
     return -EINVAL;
 }
 
 /* Fill in a file_lock structure with an appropriate FLOCK lock. */
 static void flock_make_lock(struct file *filp, struct file_lock *fl, int type)
 {
     locks_init_lock(fl);
 
     fl->fl_file = filp;
     fl->fl_owner = filp;
     fl->fl_pid = current->tgid;
     fl->fl_flags = FL_FLOCK;
     fl->fl_type = type;
     fl->fl_end = OFFSET_MAX;
 }
 
 static int assign_type(struct file_lock *fl, long type)
 {
     switch (type) {
     case F_RDLCK:
     case F_WRLCK:
     case F_UNLCK:
         fl->fl_type = type;
         break;
     default:
         return -EINVAL;
     }
     return 0;
 }
 
 static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
                  struct flock64 *l)
 {
     switch (l->l_whence) {
     case SEEK_SET:
         fl->fl_start = 0;
         break;
     case SEEK_CUR:
         fl->fl_start = filp->f_pos;
         break;
     case SEEK_END:
         fl->fl_start = i_size_read(file_inode(filp));
         break;
     default:
         return -EINVAL;
     }
     if (l->l_start > OFFSET_MAX - fl->fl_start)
         return -EOVERFLOW;
     fl->fl_start += l->l_start;
     if (fl->fl_start < 0)
         return -EINVAL;
 
     /* POSIX-1996 leaves the case l->l_len < 0 undefined;
        POSIX-2001 defines it. */
     if (l->l_len > 0) {
         if (l->l_len - 1 > OFFSET_MAX - fl->fl_start)
             return -EOVERFLOW;
         fl->fl_end = fl->fl_start + (l->l_len - 1);
 
     } else if (l->l_len < 0) {
         if (fl->fl_start + l->l_len < 0)
             return -EINVAL;
         fl->fl_end = fl->fl_start - 1;
         fl->fl_start += l->l_len;
     } else
         fl->fl_end = OFFSET_MAX;
 
     fl->fl_owner = current->files;
     fl->fl_pid = current->tgid;
     fl->fl_file = filp;
     fl->fl_flags = FL_POSIX;
     fl->fl_ops = NULL;
     fl->fl_lmops = NULL;
 
     return assign_type(fl, l->l_type);
 }
 
 /* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
  * style lock.
  */
 static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
                    struct flock *l)
 {
     struct flock64 ll = {
         .l_type = l->l_type,
         .l_whence = l->l_whence,
         .l_start = l->l_start,
         .l_len = l->l_len,
     };
 
     return flock64_to_posix_lock(filp, fl, &ll);
 }
 
 /* default lease lock manager operations */
 static bool
 lease_break_callback(struct file_lock *fl)
 {
     kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
     return false;
 }
 
 static void
 lease_setup(struct file_lock *fl, void **priv)
 {
     struct file *filp = fl->fl_file;
     struct fasync_struct *fa = *priv;
 
     /*
      * fasync_insert_entry() returns the old entry if any. If there was no
      * old entry, then it used "priv" and inserted it into the fasync list.
      * Clear the pointer to indicate that it shouldn't be freed.
      */
     if (!fasync_insert_entry(fa->fa_fd, filp, &fl->fl_fasync, fa))
         *priv = NULL;
 
     __f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);
 }
 
 static const struct lock_manager_operations lease_manager_ops = {
     .lm_break = lease_break_callback,
     .lm_change = lease_modify,
     .lm_setup = lease_setup,
 };
 
 /*
  * Initialize a lease, use the default lock manager operations
  */
 static int lease_init(struct file *filp, long type, struct file_lock *fl)
 {
     if (assign_type(fl, type) != 0)
         return -EINVAL;
 
     fl->fl_owner = filp;
     fl->fl_pid = current->tgid;
 
     fl->fl_file = filp;
     fl->fl_flags = FL_LEASE;
     fl->fl_start = 0;
     fl->fl_end = OFFSET_MAX;
     fl->fl_ops = NULL;
     fl->fl_lmops = &lease_manager_ops;
     return 0;
 }
 
 /* Allocate a file_lock initialised to this type of lease */
 static struct file_lock *lease_alloc(struct file *filp, long type)
 {
     struct file_lock *fl = locks_alloc_lock();
     int error = -ENOMEM;
 
     if (fl == NULL)
         return ERR_PTR(error);
 
     error = lease_init(filp, type, fl);
     if (error) {
         locks_free_lock(fl);
         return ERR_PTR(error);
     }
     return fl;
 }
 
 /* Check if two locks overlap each other.
  */
 static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
 {
     return ((fl1->fl_end >= fl2->fl_start) &&
         (fl2->fl_end >= fl1->fl_start));
 }
 
 /*
  * Check whether two locks have the same owner.
  */
 static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
 {
     return fl1->fl_owner == fl2->fl_owner;
 }
 
 /* Must be called with the flc_lock held! */
 static void locks_insert_global_locks(struct file_lock *fl)
 {
     struct file_lock_list_struct *fll = this_cpu_ptr(&file_lock_list);
 
     percpu_rwsem_assert_held(&file_rwsem);
 
     spin_lock(&fll->lock);
     fl->fl_link_cpu = smp_processor_id();
     hlist_add_head(&fl->fl_link, &fll->hlist);
     spin_unlock(&fll->lock);
 }
 
 /* Must be called with the flc_lock held! */
 static void locks_delete_global_locks(struct file_lock *fl)
 {
     struct file_lock_list_struct *fll;
 
     percpu_rwsem_assert_held(&file_rwsem);
 
     /*
      * Avoid taking lock if already unhashed. This is safe since this check
      * is done while holding the flc_lock, and new insertions into the list
      * also require that it be held.
      */
     if (hlist_unhashed(&fl->fl_link))
         return;
 
     fll = per_cpu_ptr(&file_lock_list, fl->fl_link_cpu);
     spin_lock(&fll->lock);
     hlist_del_init(&fl->fl_link);
     spin_unlock(&fll->lock);
 }
 
 static unsigned long
 posix_owner_key(struct file_lock *fl)
 {
     return (unsigned long)fl->fl_owner;
 }
 
 static void locks_insert_global_blocked(struct file_lock *waiter)
 {
     lockdep_assert_held(&blocked_lock_lock);
 
     hash_add(blocked_hash, &waiter->fl_link, posix_owner_key(waiter));
 }
 
 static void locks_delete_global_blocked(struct file_lock *waiter)
 {
     lockdep_assert_held(&blocked_lock_lock);
 
     hash_del(&waiter->fl_link);
 }
 
 /* Remove waiter from blocker's block list.
  * When blocker ends up pointing to itself then the list is empty.
  *
  * Must be called with blocked_lock_lock held.
  */
 static void __locks_delete_block(struct file_lock *waiter)
 {
     locks_delete_global_blocked(waiter);
     list_del_init(&waiter->fl_blocked_member);
 }
 
 static void __locks_wake_up_blocks(struct file_lock *blocker)
 {
     while (!list_empty(&blocker->fl_blocked_requests)) {
         struct file_lock *waiter;
 
         waiter = list_first_entry(&blocker->fl_blocked_requests,
                       struct file_lock, fl_blocked_member);
         __locks_delete_block(waiter);
         if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
             waiter->fl_lmops->lm_notify(waiter);
         else
             wake_up(&waiter->fl_wait);
 
         /*
          * The setting of fl_blocker to NULL marks the "done"
          * point in deleting a block. Paired with acquire at the top
          * of locks_delete_block().
          */
         smp_store_release(&waiter->fl_blocker, NULL);
     }
 }
 
 /**
  *  locks_delete_block - stop waiting for a file lock
  *  @waiter: the lock which was waiting
  *
  *  lockd/nfsd need to disconnect the lock while working on it.
  */
 int locks_delete_block(struct file_lock *waiter)
 {
     int status = -ENOENT;
 
     /*
      * If fl_blocker is NULL, it won't be set again as this thread "owns"
      * the lock and is the only one that might try to claim the lock.
      *
      * We use acquire/release to manage fl_blocker so that we can
      * optimize away taking the blocked_lock_lock in many cases.
      *
      * The smp_load_acquire guarantees two things:
      *
      * 1/ that fl_blocked_requests can be tested locklessly. If something
      * was recently added to that list it must have been in a locked region
      * *before* the locked region when fl_blocker was set to NULL.
      *
      * 2/ that no other thread is accessing 'waiter', so it is safe to free
      * it.  __locks_wake_up_blocks is careful not to touch waiter after
      * fl_blocker is released.
      *
      * If a lockless check of fl_blocker shows it to be NULL, we know that
      * no new locks can be inserted into its fl_blocked_requests list, and
      * can avoid doing anything further if the list is empty.
      */
     if (!smp_load_acquire(&waiter->fl_blocker) &&
         list_empty(&waiter->fl_blocked_requests))
         return status;
 
     spin_lock(&blocked_lock_lock);
     if (waiter->fl_blocker)
         status = 0;
     __locks_wake_up_blocks(waiter);
     __locks_delete_block(waiter);
 
     /*
      * The setting of fl_blocker to NULL marks the "done" point in deleting
      * a block. Paired with acquire at the top of this function.
      */
     smp_store_release(&waiter->fl_blocker, NULL);
     spin_unlock(&blocked_lock_lock);
     return status;
 }
 EXPORT_SYMBOL(locks_delete_block);
 
 /* Insert waiter into blocker's block list.
  * We use a circular list so that processes can be easily woken up in
  * the order they blocked. The documentation doesn't require this but
  * it seems like the reasonable thing to do.
  *
  * Must be called with both the flc_lock and blocked_lock_lock held. The
  * fl_blocked_requests list itself is protected by the blocked_lock_lock,
  * but by ensuring that the flc_lock is also held on insertions we can avoid
  * taking the blocked_lock_lock in some cases when we see that the
  * fl_blocked_requests list is empty.
  *
  * Rather than just adding to the list, we check for conflicts with any existing
  * waiters, and add beneath any waiter that blocks the new waiter.
  * Thus wakeups don't happen until needed.
  */
 static void __locks_insert_block(struct file_lock *blocker,
                  struct file_lock *waiter,
                  bool conflict(struct file_lock *,
                            struct file_lock *))
 {
     struct file_lock *fl;
     BUG_ON(!list_empty(&waiter->fl_blocked_member));
 
 new_blocker:
     list_for_each_entry(fl, &blocker->fl_blocked_requests, fl_blocked_member)
         if (conflict(fl, waiter)) {
             blocker =  fl;
             goto new_blocker;
         }
     waiter->fl_blocker = blocker;
     list_add_tail(&waiter->fl_blocked_member, &blocker->fl_blocked_requests);
     if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))
         locks_insert_global_blocked(waiter);
 
     /* The requests in waiter->fl_blocked are known to conflict with
      * waiter, but might not conflict with blocker, or the requests
      * and lock which block it.  So they all need to be woken.
      */
     __locks_wake_up_blocks(waiter);
 }
 
 /* Must be called with flc_lock held. */
 static void locks_insert_block(struct file_lock *blocker,
                    struct file_lock *waiter,
                    bool conflict(struct file_lock *,
                          struct file_lock *))
 {
     spin_lock(&blocked_lock_lock);
     __locks_insert_block(blocker, waiter, conflict);
     spin_unlock(&blocked_lock_lock);
 }
 
 /*
  * Wake up processes blocked waiting for blocker.
  *
  * Must be called with the inode->flc_lock held!
  */
 static void locks_wake_up_blocks(struct file_lock *blocker)
 {
     /*
      * Avoid taking global lock if list is empty. This is safe since new
      * blocked requests are only added to the list under the flc_lock, and
      * the flc_lock is always held here. Note that removal from the
      * fl_blocked_requests list does not require the flc_lock, so we must
      * recheck list_empty() after acquiring the blocked_lock_lock.
      */
     if (list_empty(&blocker->fl_blocked_requests))
         return;
 
     spin_lock(&blocked_lock_lock);
     __locks_wake_up_blocks(blocker);
     spin_unlock(&blocked_lock_lock);
 }
 
 static void
 locks_insert_lock_ctx(struct file_lock *fl, struct list_head *before)
 {
     list_add_tail(&fl->fl_list, before);
     locks_insert_global_locks(fl);
 }
 
 static void
 locks_unlink_lock_ctx(struct file_lock *fl)
 {
     locks_delete_global_locks(fl);
     list_del_init(&fl->fl_list);
     locks_wake_up_blocks(fl);
 }
 
 static void
 locks_delete_lock_ctx(struct file_lock *fl, struct list_head *dispose)
 {
     locks_unlink_lock_ctx(fl);
     if (dispose)
         list_add(&fl->fl_list, dispose);
     else
         locks_free_lock(fl);
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. Common functionality
  * checks for shared/exclusive status of overlapping locks.
  */
 static bool locks_conflict(struct file_lock *caller_fl,
                struct file_lock *sys_fl)
 {
     if (sys_fl->fl_type == F_WRLCK)
         return true;
     if (caller_fl->fl_type == F_WRLCK)
         return true;
     return false;
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
  * checking before calling the locks_conflict().
  */
 static bool posix_locks_conflict(struct file_lock *caller_fl,
                  struct file_lock *sys_fl)
 {
     /* POSIX locks owned by the same process do not conflict with
      * each other.
      */
     if (posix_same_owner(caller_fl, sys_fl))
         return false;
 
     /* Check whether they overlap */
     if (!locks_overlap(caller_fl, sys_fl))
         return false;
 
     return locks_conflict(caller_fl, sys_fl);
 }
 
 /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
  * checking before calling the locks_conflict().
  */
 static bool flock_locks_conflict(struct file_lock *caller_fl,
                  struct file_lock *sys_fl)
 {
     /* FLOCK locks referring to the same filp do not conflict with
      * each other.
      */
     if (caller_fl->fl_file == sys_fl->fl_file)
         return false;
 
     return locks_conflict(caller_fl, sys_fl);
 }
 
 void
 posix_test_lock(struct file *filp, struct file_lock *fl)
 {
     struct file_lock *cfl;
     struct file_lock_context *ctx;
     struct inode *inode = locks_inode(filp);
     void *owner;
     void (*func)(void);
 
     ctx = smp_load_acquire(&inode->i_flctx);
     if (!ctx || list_empty_careful(&ctx->flc_posix)) {
         fl->fl_type = F_UNLCK;
         return;
     }
 
 retry:
     spin_lock(&ctx->flc_lock);
     list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
         if (!posix_locks_conflict(fl, cfl))
             continue;
         if (cfl->fl_lmops && cfl->fl_lmops->lm_lock_expirable
             && (*cfl->fl_lmops->lm_lock_expirable)(cfl)) {
             owner = cfl->fl_lmops->lm_mod_owner;
             func = cfl->fl_lmops->lm_expire_lock;
             __module_get(owner);
             spin_unlock(&ctx->flc_lock);
             (*func)();
             module_put(owner);
             goto retry;
         }
         locks_copy_conflock(fl, cfl);
         goto out;
     }
     fl->fl_type = F_UNLCK;
 out:
     spin_unlock(&ctx->flc_lock);
     return;
 }
 EXPORT_SYMBOL(posix_test_lock);
 
 /*
  * Deadlock detection:
  *
  * We attempt to detect deadlocks that are due purely to posix file
  * locks.
  *
  * We assume that a task can be waiting for at most one lock at a time.
  * So for any acquired lock, the process holding that lock may be
  * waiting on at most one other lock.  That lock in turns may be held by
  * someone waiting for at most one other lock.  Given a requested lock
  * caller_fl which is about to wait for a conflicting lock block_fl, we
  * follow this chain of waiters to ensure we are not about to create a
  * cycle.
  *
  * Since we do this before we ever put a process to sleep on a lock, we
  * are ensured that there is never a cycle; that is what guarantees that
  * the while() loop in posix_locks_deadlock() eventually completes.
  *
  * Note: the above assumption may not be true when handling lock
  * requests from a broken NFS client. It may also fail in the presence
  * of tasks (such as posix threads) sharing the same open file table.
  * To handle those cases, we just bail out after a few iterations.
  *
  * For FL_OFDLCK locks, the owner is the filp, not the files_struct.
  * Because the owner is not even nominally tied to a thread of
  * execution, the deadlock detection below can't reasonably work well. Just
  * skip it for those.
  *
  * In principle, we could do a more limited deadlock detection on FL_OFDLCK
  * locks that just checks for the case where two tasks are attempting to
  * upgrade from read to write locks on the same inode.
  */
 
 #define MAX_DEADLK_ITERATIONS 10
 
 /* Find a lock that the owner of the given block_fl is blocking on. */
 static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
 {
     struct file_lock *fl;
 
     hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) {
         if (posix_same_owner(fl, block_fl)) {
             while (fl->fl_blocker)
                 fl = fl->fl_blocker;
             return fl;
         }
     }
     return NULL;
 }
 
 /* Must be called with the blocked_lock_lock held! */
 static int posix_locks_deadlock(struct file_lock *caller_fl,
                 struct file_lock *block_fl)
 {
     int i = 0;
 
     lockdep_assert_held(&blocked_lock_lock);
 
     /*
      * This deadlock detector can't reasonably detect deadlocks with
      * FL_OFDLCK locks, since they aren't owned by a process, per-se.
      */
     if (IS_OFDLCK(caller_fl))
         return 0;
 
     while ((block_fl = what_owner_is_waiting_for(block_fl))) {
         if (i++ > MAX_DEADLK_ITERATIONS)
             return 0;
         if (posix_same_owner(caller_fl, block_fl))
             return 1;
     }
     return 0;
 }
 
 /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
  * after any leases, but before any posix locks.
  *
  * Note that if called with an FL_EXISTS argument, the caller may determine
  * whether or not a lock was successfully freed by testing the return
  * value for -ENOENT.
  */
 static int flock_lock_inode(struct inode *inode, struct file_lock *request)
 {
     struct file_lock *new_fl = NULL;
     struct file_lock *fl;
     struct file_lock_context *ctx;
     int error = 0;
     bool found = false;
     LIST_HEAD(dispose);
 
     ctx = locks_get_lock_context(inode, request->fl_type);
     if (!ctx) {
         if (request->fl_type != F_UNLCK)
             return -ENOMEM;
         return (request->fl_flags & FL_EXISTS) ? -ENOENT : 0;
     }
 
     if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {
         new_fl = locks_alloc_lock();
         if (!new_fl)
             return -ENOMEM;
     }
 
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
     if (request->fl_flags & FL_ACCESS)
         goto find_conflict;
 
     list_for_each_entry(fl, &ctx->flc_flock, fl_list) {
         if (request->fl_file != fl->fl_file)
             continue;
         if (request->fl_type == fl->fl_type)
             goto out;
         found = true;
         locks_delete_lock_ctx(fl, &dispose);
         break;
     }
 
     if (request->fl_type == F_UNLCK) {
         if ((request->fl_flags & FL_EXISTS) && !found)
             error = -ENOENT;
         goto out;
     }
 
 find_conflict:
     list_for_each_entry(fl, &ctx->flc_flock, fl_list) {
         if (!flock_locks_conflict(request, fl))
             continue;
         error = -EAGAIN;
         if (!(request->fl_flags & FL_SLEEP))
             goto out;
         error = FILE_LOCK_DEFERRED;
         locks_insert_block(fl, request, flock_locks_conflict);
         goto out;
     }
     if (request->fl_flags & FL_ACCESS)
         goto out;
     locks_copy_lock(new_fl, request);
     locks_move_blocks(new_fl, request);
     locks_insert_lock_ctx(new_fl, &ctx->flc_flock);
     new_fl = NULL;
     error = 0;
 
 out:
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
     if (new_fl)
         locks_free_lock(new_fl);
     locks_dispose_list(&dispose);
     trace_flock_lock_inode(inode, request, error);
     return error;
 }
 
 static int posix_lock_inode(struct inode *inode, struct file_lock *request,
                 struct file_lock *conflock)
 {
     struct file_lock *fl, *tmp;
     struct file_lock *new_fl = NULL;
     struct file_lock *new_fl2 = NULL;
     struct file_lock *left = NULL;
     struct file_lock *right = NULL;
     struct file_lock_context *ctx;
     int error;
     bool added = false;
     LIST_HEAD(dispose);
     void *owner;
     void (*func)(void);
 
     ctx = locks_get_lock_context(inode, request->fl_type);
     if (!ctx)
         return (request->fl_type == F_UNLCK) ? 0 : -ENOMEM;
 
     /*
      * We may need two file_lock structures for this operation,
      * so we get them in advance to avoid races.
      *
      * In some cases we can be sure, that no new locks will be needed
      */
     if (!(request->fl_flags & FL_ACCESS) &&
         (request->fl_type != F_UNLCK ||
          request->fl_start != 0 || request->fl_end != OFFSET_MAX)) {
         new_fl = locks_alloc_lock();
         new_fl2 = locks_alloc_lock();
     }
 
 retry:
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
     /*
      * New lock request. Walk all POSIX locks and look for conflicts. If
      * there are any, either return error or put the request on the
      * blocker's list of waiters and the global blocked_hash.
      */
     if (request->fl_type != F_UNLCK) {
         list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
             if (!posix_locks_conflict(request, fl))
                 continue;
             if (fl->fl_lmops && fl->fl_lmops->lm_lock_expirable
                 && (*fl->fl_lmops->lm_lock_expirable)(fl)) {
                 owner = fl->fl_lmops->lm_mod_owner;
                 func = fl->fl_lmops->lm_expire_lock;
                 __module_get(owner);
                 spin_unlock(&ctx->flc_lock);
                 percpu_up_read(&file_rwsem);
                 (*func)();
                 module_put(owner);
                 goto retry;
             }
             if (conflock)
                 locks_copy_conflock(conflock, fl);
             error = -EAGAIN;
             if (!(request->fl_flags & FL_SLEEP))
                 goto out;
             /*
              * Deadlock detection and insertion into the blocked
              * locks list must be done while holding the same lock!
              */
             error = -EDEADLK;
             spin_lock(&blocked_lock_lock);
             /*
              * Ensure that we don't find any locks blocked on this
              * request during deadlock detection.
              */
             __locks_wake_up_blocks(request);
             if (likely(!posix_locks_deadlock(request, fl))) {
                 error = FILE_LOCK_DEFERRED;
                 __locks_insert_block(fl, request,
                              posix_locks_conflict);
             }
             spin_unlock(&blocked_lock_lock);
             goto out;
         }
     }
 
     /* If we're just looking for a conflict, we're done. */
     error = 0;
     if (request->fl_flags & FL_ACCESS)
         goto out;
 
     /* Find the first old lock with the same owner as the new lock */
     list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
         if (posix_same_owner(request, fl))
             break;
     }
 
     /* Process locks with this owner. */
     list_for_each_entry_safe_from(fl, tmp, &ctx->flc_posix, fl_list) {
         if (!posix_same_owner(request, fl))
             break;
 
         /* Detect adjacent or overlapping regions (if same lock type) */
         if (request->fl_type == fl->fl_type) {
             /* In all comparisons of start vs end, use
              * "start - 1" rather than "end + 1". If end
              * is OFFSET_MAX, end + 1 will become negative.
              */
             if (fl->fl_end < request->fl_start - 1)
                 continue;
             /* If the next lock in the list has entirely bigger
              * addresses than the new one, insert the lock here.
              */
             if (fl->fl_start - 1 > request->fl_end)
                 break;
 
             /* If we come here, the new and old lock are of the
              * same type and adjacent or overlapping. Make one
              * lock yielding from the lower start address of both
              * locks to the higher end address.
              */
             if (fl->fl_start > request->fl_start)
                 fl->fl_start = request->fl_start;
             else
                 request->fl_start = fl->fl_start;
             if (fl->fl_end < request->fl_end)
                 fl->fl_end = request->fl_end;
             else
                 request->fl_end = fl->fl_end;
             if (added) {
                 locks_delete_lock_ctx(fl, &dispose);
                 continue;
             }
             request = fl;
             added = true;
         } else {
             /* Processing for different lock types is a bit
              * more complex.
              */
             if (fl->fl_end < request->fl_start)
                 continue;
             if (fl->fl_start > request->fl_end)
                 break;
             if (request->fl_type == F_UNLCK)
                 added = true;
             if (fl->fl_start < request->fl_start)
                 left = fl;
             /* If the next lock in the list has a higher end
              * address than the new one, insert the new one here.
              */
             if (fl->fl_end > request->fl_end) {
                 right = fl;
                 break;
             }
             if (fl->fl_start >= request->fl_start) {
                 /* The new lock completely replaces an old
                  * one (This may happen several times).
                  */
                 if (added) {
                     locks_delete_lock_ctx(fl, &dispose);
                     continue;
                 }
                 /*
                  * Replace the old lock with new_fl, and
                  * remove the old one. It's safe to do the
                  * insert here since we know that we won't be
                  * using new_fl later, and that the lock is
                  * just replacing an existing lock.
                  */
                 error = -ENOLCK;
                 if (!new_fl)
                     goto out;
                 locks_copy_lock(new_fl, request);
                 locks_move_blocks(new_fl, request);
                 request = new_fl;
                 new_fl = NULL;
                 locks_insert_lock_ctx(request, &fl->fl_list);
                 locks_delete_lock_ctx(fl, &dispose);
                 added = true;
             }
         }
     }
 
     /*
      * The above code only modifies existing locks in case of merging or
      * replacing. If new lock(s) need to be inserted all modifications are
      * done below this, so it's safe yet to bail out.
      */
     error = -ENOLCK; /* "no luck" */
     if (right && left == right && !new_fl2)
         goto out;
 
     error = 0;
     if (!added) {
         if (request->fl_type == F_UNLCK) {
             if (request->fl_flags & FL_EXISTS)
                 error = -ENOENT;
             goto out;
         }
 
         if (!new_fl) {
             error = -ENOLCK;
             goto out;
         }
         locks_copy_lock(new_fl, request);
         locks_move_blocks(new_fl, request);
         locks_insert_lock_ctx(new_fl, &fl->fl_list);
         fl = new_fl;
         new_fl = NULL;
     }
     if (right) {
         if (left == right) {
             /* The new lock breaks the old one in two pieces,
              * so we have to use the second new lock.
              */
             left = new_fl2;
             new_fl2 = NULL;
             locks_copy_lock(left, right);
             locks_insert_lock_ctx(left, &fl->fl_list);
         }
         right->fl_start = request->fl_end + 1;
         locks_wake_up_blocks(right);
     }
     if (left) {
         left->fl_end = request->fl_start - 1;
         locks_wake_up_blocks(left);
     }
  out:
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
     /*
      * Free any unused locks.
      */
     if (new_fl)
         locks_free_lock(new_fl);
     if (new_fl2)
         locks_free_lock(new_fl2);
     locks_dispose_list(&dispose);
     trace_posix_lock_inode(inode, request, error);
 
     return error;
 }
 
 /**
  * posix_lock_file - Apply a POSIX-style lock to a file
  * @filp: The file to apply the lock to
  * @fl: The lock to be applied
  * @conflock: Place to return a copy of the conflicting lock, if found.
  *
  * Add a POSIX style lock to a file.
  * We merge adjacent & overlapping locks whenever possible.
  * POSIX locks are sorted by owner task, then by starting address
  *
  * Note that if called with an FL_EXISTS argument, the caller may determine
  * whether or not a lock was successfully freed by testing the return
  * value for -ENOENT.
  */
 int posix_lock_file(struct file *filp, struct file_lock *fl,
             struct file_lock *conflock)
 {
     return posix_lock_inode(locks_inode(filp), fl, conflock);
 }
 EXPORT_SYMBOL(posix_lock_file);
 
 /**
  * posix_lock_inode_wait - Apply a POSIX-style lock to a file
  * @inode: inode of file to which lock request should be applied
  * @fl: The lock to be applied
  *
  * Apply a POSIX style lock request to an inode.
  */
 static int posix_lock_inode_wait(struct inode *inode, struct file_lock *fl)
 {
     int error;
     might_sleep ();
     for (;;) {
         error = posix_lock_inode(inode, fl, NULL);
         if (error != FILE_LOCK_DEFERRED)
             break;
         error = wait_event_interruptible(fl->fl_wait,
                     list_empty(&fl->fl_blocked_member));
         if (error)
             break;
     }
     locks_delete_block(fl);
     return error;
 }
 
 static void lease_clear_pending(struct file_lock *fl, int arg)
 {
     switch (arg) {
     case F_UNLCK:
         fl->fl_flags &= ~FL_UNLOCK_PENDING;
         fallthrough;
     case F_RDLCK:
         fl->fl_flags &= ~FL_DOWNGRADE_PENDING;
     }
 }
 
 /* We already had a lease on this file; just change its type */
 int lease_modify(struct file_lock *fl, int arg, struct list_head *dispose)
 {
     int error = assign_type(fl, arg);
 
     if (error)
         return error;
     lease_clear_pending(fl, arg);
     locks_wake_up_blocks(fl);
     if (arg == F_UNLCK) {
         struct file *filp = fl->fl_file;
 
         f_delown(filp);
         filp->f_owner.signum = 0;
         fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
         if (fl->fl_fasync != NULL) {
             printk(KERN_ERR "locks_delete_lock: fasync == %p\n", fl->fl_fasync);
             fl->fl_fasync = NULL;
         }
         locks_delete_lock_ctx(fl, dispose);
     }
     return 0;
 }
 EXPORT_SYMBOL(lease_modify);
 
 static bool past_time(unsigned long then)
 {
     if (!then)
         /* 0 is a special value meaning "this never expires": */
         return false;
     return time_after(jiffies, then);
 }
 
 static void time_out_leases(struct inode *inode, struct list_head *dispose)
 {
     struct file_lock_context *ctx = inode->i_flctx;
     struct file_lock *fl, *tmp;
 
     lockdep_assert_held(&ctx->flc_lock);
 
     list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list) {
         trace_time_out_leases(inode, fl);
         if (past_time(fl->fl_downgrade_time))
             lease_modify(fl, F_RDLCK, dispose);
         if (past_time(fl->fl_break_time))
             lease_modify(fl, F_UNLCK, dispose);
     }
 }
 
 static bool leases_conflict(struct file_lock *lease, struct file_lock *breaker)
 {
     bool rc;
 
     if (lease->fl_lmops->lm_breaker_owns_lease
             && lease->fl_lmops->lm_breaker_owns_lease(lease))
         return false;
     if ((breaker->fl_flags & FL_LAYOUT) != (lease->fl_flags & FL_LAYOUT)) {
         rc = false;
         goto trace;
     }
     if ((breaker->fl_flags & FL_DELEG) && (lease->fl_flags & FL_LEASE)) {
         rc = false;
         goto trace;
     }
 
     rc = locks_conflict(breaker, lease);
 trace:
     trace_leases_conflict(rc, lease, breaker);
     return rc;
 }
 
 static bool
 any_leases_conflict(struct inode *inode, struct file_lock *breaker)
 {
     struct file_lock_context *ctx = inode->i_flctx;
     struct file_lock *fl;
 
     lockdep_assert_held(&ctx->flc_lock);
 
     list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
         if (leases_conflict(fl, breaker))
             return true;
     }
     return false;
 }
 
 /**
  *  __break_lease   -   revoke all outstanding leases on file
  *  @inode: the inode of the file to return
  *  @mode: O_RDONLY: break only write leases; O_WRONLY or O_RDWR:
  *      break all leases
  *  @type: FL_LEASE: break leases and delegations; FL_DELEG: break
  *      only delegations
  *
  *  break_lease (inlined for speed) has checked there already is at least
  *  some kind of lock (maybe a lease) on this file.  Leases are broken on
  *  a call to open() or truncate().  This function can sleep unless you
  *  specified %O_NONBLOCK to your open().
  */
 int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
 {
     int error = 0;
     struct file_lock_context *ctx;
     struct file_lock *new_fl, *fl, *tmp;
     unsigned long break_time;
     int want_write = (mode & O_ACCMODE) != O_RDONLY;
     LIST_HEAD(dispose);
 
     new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);
     if (IS_ERR(new_fl))
         return PTR_ERR(new_fl);
     new_fl->fl_flags = type;
 
     /* typically we will check that ctx is non-NULL before calling */
     ctx = smp_load_acquire(&inode->i_flctx);
     if (!ctx) {
         WARN_ON_ONCE(1);
         goto free_lock;
     }
 
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
 
     time_out_leases(inode, &dispose);
 
     if (!any_leases_conflict(inode, new_fl))
         goto out;
 
     break_time = 0;
     if (lease_break_time > 0) {
         break_time = jiffies + lease_break_time * HZ;
         if (break_time == 0)
             break_time++;   /* so that 0 means no break time */
     }
 
     list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list) {
         if (!leases_conflict(fl, new_fl))
             continue;
         if (want_write) {
             if (fl->fl_flags & FL_UNLOCK_PENDING)
                 continue;
             fl->fl_flags |= FL_UNLOCK_PENDING;
             fl->fl_break_time = break_time;
         } else {
             if (lease_breaking(fl))
                 continue;
             fl->fl_flags |= FL_DOWNGRADE_PENDING;
             fl->fl_downgrade_time = break_time;
         }
         if (fl->fl_lmops->lm_break(fl))
             locks_delete_lock_ctx(fl, &dispose);
     }
 
     if (list_empty(&ctx->flc_lease))
         goto out;
 
     if (mode & O_NONBLOCK) {
         trace_break_lease_noblock(inode, new_fl);
         error = -EWOULDBLOCK;
         goto out;
     }
 
 restart:
     fl = list_first_entry(&ctx->flc_lease, struct file_lock, fl_list);
     break_time = fl->fl_break_time;
     if (break_time != 0)
         break_time -= jiffies;
     if (break_time == 0)
         break_time++;
     locks_insert_block(fl, new_fl, leases_conflict);
     trace_break_lease_block(inode, new_fl);
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
 
     locks_dispose_list(&dispose);
     error = wait_event_interruptible_timeout(new_fl->fl_wait,
                     list_empty(&new_fl->fl_blocked_member),
                     break_time);
 
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
     trace_break_lease_unblock(inode, new_fl);
     locks_delete_block(new_fl);
     if (error >= 0) {
         /*
          * Wait for the next conflicting lease that has not been
          * broken yet
          */
         if (error == 0)
             time_out_leases(inode, &dispose);
         if (any_leases_conflict(inode, new_fl))
             goto restart;
         error = 0;
     }
 out:
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
     locks_dispose_list(&dispose);
 free_lock:
     locks_free_lock(new_fl);
     return error;
 }
 EXPORT_SYMBOL(__break_lease);
 
 /**
  *  lease_get_mtime - update modified time of an inode with exclusive lease
  *  @inode: the inode
  *      @time:  pointer to a timespec which contains the last modified time
  *
  * This is to force NFS clients to flush their caches for files with
  * exclusive leases.  The justification is that if someone has an
  * exclusive lease, then they could be modifying it.
  */
 void lease_get_mtime(struct inode *inode, struct timespec64 *time)
 {
     bool has_lease = false;
     struct file_lock_context *ctx;
     struct file_lock *fl;
 
     ctx = smp_load_acquire(&inode->i_flctx);
     if (ctx && !list_empty_careful(&ctx->flc_lease)) {
         spin_lock(&ctx->flc_lock);
         fl = list_first_entry_or_null(&ctx->flc_lease,
                           struct file_lock, fl_list);
         if (fl && (fl->fl_type == F_WRLCK))
             has_lease = true;
         spin_unlock(&ctx->flc_lock);
     }
 
     if (has_lease)
         *time = current_time(inode);
 }
 EXPORT_SYMBOL(lease_get_mtime);
 
 /**
  *  fcntl_getlease - Enquire what lease is currently active
  *  @filp: the file
  *
  *  The value returned by this function will be one of
  *  (if no lease break is pending):
  *
  *  %F_RDLCK to indicate a shared lease is held.
  *
  *  %F_WRLCK to indicate an exclusive lease is held.
  *
  *  %F_UNLCK to indicate no lease is held.
  *
  *  (if a lease break is pending):
  *
  *  %F_RDLCK to indicate an exclusive lease needs to be
  *      changed to a shared lease (or removed).
  *
  *  %F_UNLCK to indicate the lease needs to be removed.
  *
  *  XXX: sfr & willy disagree over whether F_INPROGRESS
  *  should be returned to userspace.
  */
 int fcntl_getlease(struct file *filp)
 {
     struct file_lock *fl;
     struct inode *inode = locks_inode(filp);
     struct file_lock_context *ctx;
     int type = F_UNLCK;
     LIST_HEAD(dispose);
 
     ctx = smp_load_acquire(&inode->i_flctx);
     if (ctx && !list_empty_careful(&ctx->flc_lease)) {
         percpu_down_read(&file_rwsem);
         spin_lock(&ctx->flc_lock);
         time_out_leases(inode, &dispose);
         list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
             if (fl->fl_file != filp)
                 continue;
             type = target_leasetype(fl);
             break;
         }
         spin_unlock(&ctx->flc_lock);
         percpu_up_read(&file_rwsem);
 
         locks_dispose_list(&dispose);
     }
     return type;
 }
 
 /**
  * check_conflicting_open - see if the given file points to an inode that has
  *              an existing open that would conflict with the
  *              desired lease.
  * @filp:   file to check
  * @arg:    type of lease that we're trying to acquire
  * @flags:  current lock flags
  *
  * Check to see if there's an existing open fd on this file that would
  * conflict with the lease we're trying to set.
  */
 static int
 check_conflicting_open(struct file *filp, const long arg, int flags)
 {
     struct inode *inode = locks_inode(filp);
     int self_wcount = 0, self_rcount = 0;
 
     if (flags & FL_LAYOUT)
         return 0;
     if (flags & FL_DELEG)
         /* We leave these checks to the caller */
         return 0;
 
     if (arg == F_RDLCK)
         return inode_is_open_for_write(inode) ? -EAGAIN : 0;
     else if (arg != F_WRLCK)
         return 0;
 
     /*
      * Make sure that only read/write count is from lease requestor.
      * Note that this will result in denying write leases when i_writecount
      * is negative, which is what we want.  (We shouldn't grant write leases
      * on files open for execution.)
      */
     if (filp->f_mode & FMODE_WRITE)
         self_wcount = 1;
     else if (filp->f_mode & FMODE_READ)
         self_rcount = 1;
 
     if (atomic_read(&inode->i_writecount) != self_wcount ||
         atomic_read(&inode->i_readcount) != self_rcount)
         return -EAGAIN;
 
     return 0;
 }
 
 static int
 generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **priv)
 {
     struct file_lock *fl, *my_fl = NULL, *lease;
     struct inode *inode = locks_inode(filp);
     struct file_lock_context *ctx;
     bool is_deleg = (*flp)->fl_flags & FL_DELEG;
     int error;
     LIST_HEAD(dispose);
 
     lease = *flp;
     trace_generic_add_lease(inode, lease);
 
     /* Note that arg is never F_UNLCK here */
     ctx = locks_get_lock_context(inode, arg);
     if (!ctx)
         return -ENOMEM;
 
     /*
      * In the delegation case we need mutual exclusion with
      * a number of operations that take the i_mutex.  We trylock
      * because delegations are an optional optimization, and if
      * there's some chance of a conflict--we'd rather not
      * bother, maybe that's a sign this just isn't a good file to
      * hand out a delegation on.
      */
     if (is_deleg && !inode_trylock(inode))
         return -EAGAIN;
 
     if (is_deleg && arg == F_WRLCK) {
         /* Write delegations are not currently supported: */
         inode_unlock(inode);
         WARN_ON_ONCE(1);
         return -EINVAL;
     }
 
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
     time_out_leases(inode, &dispose);
     error = check_conflicting_open(filp, arg, lease->fl_flags);
     if (error)
         goto out;
 
     /*
      * At this point, we know that if there is an exclusive
      * lease on this file, then we hold it on this filp
      * (otherwise our open of this file would have blocked).
      * And if we are trying to acquire an exclusive lease,
      * then the file is not open by anyone (including us)
      * except for this filp.
      */
     error = -EAGAIN;
     list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
         if (fl->fl_file == filp &&
             fl->fl_owner == lease->fl_owner) {
             my_fl = fl;
             continue;
         }
 
         /*
          * No exclusive leases if someone else has a lease on
          * this file:
          */
         if (arg == F_WRLCK)
             goto out;
         /*
          * Modifying our existing lease is OK, but no getting a
          * new lease if someone else is opening for write:
          */
         if (fl->fl_flags & FL_UNLOCK_PENDING)
             goto out;
     }
 
     if (my_fl != NULL) {
         lease = my_fl;
         error = lease->fl_lmops->lm_change(lease, arg, &dispose);
         if (error)
             goto out;
         goto out_setup;
     }
 
     error = -EINVAL;
     if (!leases_enable)
         goto out;
 
     locks_insert_lock_ctx(lease, &ctx->flc_lease);
     /*
      * The check in break_lease() is lockless. It's possible for another
      * open to race in after we did the earlier check for a conflicting
      * open but before the lease was inserted. Check again for a
      * conflicting open and cancel the lease if there is one.
      *
      * We also add a barrier here to ensure that the insertion of the lock
      * precedes these checks.
      */
     smp_mb();
     error = check_conflicting_open(filp, arg, lease->fl_flags);
     if (error) {
         locks_unlink_lock_ctx(lease);
         goto out;
     }
 
 out_setup:
     if (lease->fl_lmops->lm_setup)
         lease->fl_lmops->lm_setup(lease, priv);
 out:
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
     locks_dispose_list(&dispose);
     if (is_deleg)
         inode_unlock(inode);
     if (!error && !my_fl)
         *flp = NULL;
     return error;
 }
 
 static int generic_delete_lease(struct file *filp, void *owner)
 {
     int error = -EAGAIN;
     struct file_lock *fl, *victim = NULL;
     struct inode *inode = locks_inode(filp);
     struct file_lock_context *ctx;
     LIST_HEAD(dispose);
 
     ctx = smp_load_acquire(&inode->i_flctx);
     if (!ctx) {
         trace_generic_delete_lease(inode, NULL);
         return error;
     }
 
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
     list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
         if (fl->fl_file == filp &&
             fl->fl_owner == owner) {
             victim = fl;
             break;
         }
     }
     trace_generic_delete_lease(inode, victim);
     if (victim)
         error = fl->fl_lmops->lm_change(victim, F_UNLCK, &dispose);
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
     locks_dispose_list(&dispose);
     return error;
 }
 
 /**
  *  generic_setlease    -   sets a lease on an open file
  *  @filp:  file pointer
  *  @arg:   type of lease to obtain
  *  @flp:   input - file_lock to use, output - file_lock inserted
  *  @priv:  private data for lm_setup (may be NULL if lm_setup
  *      doesn't require it)
  *
  *  The (input) flp->fl_lmops->lm_break function is required
  *  by break_lease().
  */
 int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
             void **priv)
 {
     struct inode *inode = locks_inode(filp);
     int error;
 
     if ((!uid_eq(current_fsuid(), inode->i_uid)) && !capable(CAP_LEASE))
         return -EACCES;
     if (!S_ISREG(inode->i_mode))
         return -EINVAL;
     error = security_file_lock(filp, arg);
     if (error)
         return error;
 
     switch (arg) {
     case F_UNLCK:
         return generic_delete_lease(filp, *priv);
     case F_RDLCK:
     case F_WRLCK:
         if (!(*flp)->fl_lmops->lm_break) {
             WARN_ON_ONCE(1);
             return -ENOLCK;
         }
 
         return generic_add_lease(filp, arg, flp, priv);
     default:
         return -EINVAL;
     }
 }
 EXPORT_SYMBOL(generic_setlease);
 
 #if IS_ENABLED(CONFIG_SRCU)
 /*
  * Kernel subsystems can register to be notified on any attempt to set
  * a new lease with the lease_notifier_chain. This is used by (e.g.) nfsd
  * to close files that it may have cached when there is an attempt to set a
  * conflicting lease.
  */
 static struct srcu_notifier_head lease_notifier_chain;
 
 static inline void
 lease_notifier_chain_init(void)
 {
     srcu_init_notifier_head(&lease_notifier_chain);
 }
 
 static inline void
 setlease_notifier(long arg, struct file_lock *lease)
 {
     if (arg != F_UNLCK)
         srcu_notifier_call_chain(&lease_notifier_chain, arg, lease);
 }
 
 int lease_register_notifier(struct notifier_block *nb)
 {
     return srcu_notifier_chain_register(&lease_notifier_chain, nb);
 }
 EXPORT_SYMBOL_GPL(lease_register_notifier);
 
 void lease_unregister_notifier(struct notifier_block *nb)
 {
     srcu_notifier_chain_unregister(&lease_notifier_chain, nb);
 }
 EXPORT_SYMBOL_GPL(lease_unregister_notifier);
 
 #else /* !IS_ENABLED(CONFIG_SRCU) */
 static inline void
 lease_notifier_chain_init(void)
 {
 }
 
 static inline void
 setlease_notifier(long arg, struct file_lock *lease)
 {
 }
 
 int lease_register_notifier(struct notifier_block *nb)
 {
     return 0;
 }
 EXPORT_SYMBOL_GPL(lease_register_notifier);
 
 void lease_unregister_notifier(struct notifier_block *nb)
 {
 }
 EXPORT_SYMBOL_GPL(lease_unregister_notifier);
 
 #endif /* IS_ENABLED(CONFIG_SRCU) */
 
 /**
  * vfs_setlease        -       sets a lease on an open file
  * @filp:   file pointer
  * @arg:    type of lease to obtain
  * @lease:  file_lock to use when adding a lease
  * @priv:   private info for lm_setup when adding a lease (may be
  *      NULL if lm_setup doesn't require it)
  *
  * Call this to establish a lease on the file. The "lease" argument is not
  * used for F_UNLCK requests and may be NULL. For commands that set or alter
  * an existing lease, the ``(*lease)->fl_lmops->lm_break`` operation must be
  * set; if not, this function will return -ENOLCK (and generate a scary-looking
  * stack trace).
  *
  * The "priv" pointer is passed directly to the lm_setup function as-is. It
  * may be NULL if the lm_setup operation doesn't require it.
  */
 int
 vfs_setlease(struct file *filp, long arg, struct file_lock **lease, void **priv)
 {
     if (lease)
         setlease_notifier(arg, *lease);
     if (filp->f_op->setlease)
         return filp->f_op->setlease(filp, arg, lease, priv);
     else
         return generic_setlease(filp, arg, lease, priv);
 }
 EXPORT_SYMBOL_GPL(vfs_setlease);
 
 static int do_fcntl_add_lease(unsigned int fd, struct file *filp, long arg)
 {
     struct file_lock *fl;
     struct fasync_struct *new;
     int error;
 
     fl = lease_alloc(filp, arg);
     if (IS_ERR(fl))
         return PTR_ERR(fl);
 
     new = fasync_alloc();
     if (!new) {
         locks_free_lock(fl);
         return -ENOMEM;
     }
     new->fa_fd = fd;
 
     error = vfs_setlease(filp, arg, &fl, (void **)&new);
     if (fl)
         locks_free_lock(fl);
     if (new)
         fasync_free(new);
     return error;
 }
 
 /**
  *  fcntl_setlease  -   sets a lease on an open file
  *  @fd: open file descriptor
  *  @filp: file pointer
  *  @arg: type of lease to obtain
  *
  *  Call this fcntl to establish a lease on the file.
  *  Note that you also need to call %F_SETSIG to
  *  receive a signal when the lease is broken.
  */
 int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
 {
     if (arg == F_UNLCK)
         return vfs_setlease(filp, F_UNLCK, NULL, (void **)&filp);
     return do_fcntl_add_lease(fd, filp, arg);
 }
 
 /**
  * flock_lock_inode_wait - Apply a FLOCK-style lock to a file
  * @inode: inode of the file to apply to
  * @fl: The lock to be applied
  *
  * Apply a FLOCK style lock request to an inode.
  */
 static int flock_lock_inode_wait(struct inode *inode, struct file_lock *fl)
 {
     int error;
     might_sleep();
     for (;;) {
         error = flock_lock_inode(inode, fl);
         if (error != FILE_LOCK_DEFERRED)
             break;
         error = wait_event_interruptible(fl->fl_wait,
                 list_empty(&fl->fl_blocked_member));
         if (error)
             break;
     }
     locks_delete_block(fl);
     return error;
 }
 
 /**
  * locks_lock_inode_wait - Apply a lock to an inode
  * @inode: inode of the file to apply to
  * @fl: The lock to be applied
  *
  * Apply a POSIX or FLOCK style lock request to an inode.
  */
 int locks_lock_inode_wait(struct inode *inode, struct file_lock *fl)
 {
     int res = 0;
     switch (fl->fl_flags & (FL_POSIX|FL_FLOCK)) {
         case FL_POSIX:
             res = posix_lock_inode_wait(inode, fl);
             break;
         case FL_FLOCK:
             res = flock_lock_inode_wait(inode, fl);
             break;
         default:
             BUG();
     }
     return res;
 }
 EXPORT_SYMBOL(locks_lock_inode_wait);
 
 /**
  *  sys_flock: - flock() system call.
  *  @fd: the file descriptor to lock.
  *  @cmd: the type of lock to apply.
  *
  *  Apply a %FL_FLOCK style lock to an open file descriptor.
  *  The @cmd can be one of:
  *
  *  - %LOCK_SH -- a shared lock.
  *  - %LOCK_EX -- an exclusive lock.
  *  - %LOCK_UN -- remove an existing lock.
  *  - %LOCK_MAND -- a 'mandatory' flock. (DEPRECATED)
  *
  *  %LOCK_MAND support has been removed from the kernel.
  */
 SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
 {
     int can_sleep, error, type;
     struct file_lock fl;
     struct fd f;
 
     /*
      * LOCK_MAND locks were broken for a long time in that they never
      * conflicted with one another and didn't prevent any sort of open,
      * read or write activity.
      *
      * Just ignore these requests now, to preserve legacy behavior, but
      * throw a warning to let people know that they don't actually work.
      */
     if (cmd & LOCK_MAND) {
         pr_warn_once("Attempt to set a LOCK_MAND lock via flock(2). This support has been removed and the request ignored.\n");
         return 0;
     }
 
     type = flock_translate_cmd(cmd & ~LOCK_NB);
     if (type < 0)
         return type;
 
     error = -EBADF;
     f = fdget(fd);
     if (!f.file)
         return error;
 
     if (type != F_UNLCK && !(f.file->f_mode & (FMODE_READ | FMODE_WRITE)))
         goto out_putf;
 
     flock_make_lock(f.file, &fl, type);
 
     error = security_file_lock(f.file, fl.fl_type);
     if (error)
         goto out_putf;
 
     can_sleep = !(cmd & LOCK_NB);
     if (can_sleep)
         fl.fl_flags |= FL_SLEEP;
 
     if (f.file->f_op->flock)
         error = f.file->f_op->flock(f.file,
                         (can_sleep) ? F_SETLKW : F_SETLK,
                         &fl);
     else
         error = locks_lock_file_wait(f.file, &fl);
 
     locks_release_private(&fl);
  out_putf:
     fdput(f);
 
     return error;
 }
 
 /**
  * vfs_test_lock - test file byte range lock
  * @filp: The file to test lock for
  * @fl: The lock to test; also used to hold result
  *
  * Returns -ERRNO on failure.  Indicates presence of conflicting lock by
  * setting conf->fl_type to something other than F_UNLCK.
  */
 int vfs_test_lock(struct file *filp, struct file_lock *fl)
 {
     if (filp->f_op->lock)
         return filp->f_op->lock(filp, F_GETLK, fl);
     posix_test_lock(filp, fl);
     return 0;
 }
 EXPORT_SYMBOL_GPL(vfs_test_lock);
 
 /**
  * locks_translate_pid - translate a file_lock's fl_pid number into a namespace
  * @fl: The file_lock who's fl_pid should be translated
  * @ns: The namespace into which the pid should be translated
  *
  * Used to tranlate a fl_pid into a namespace virtual pid number
  */
 static pid_t locks_translate_pid(struct file_lock *fl, struct pid_namespace *ns)
 {
     pid_t vnr;
     struct pid *pid;
 
     if (IS_OFDLCK(fl))
         return -1;
     if (IS_REMOTELCK(fl))
         return fl->fl_pid;
     /*
      * If the flock owner process is dead and its pid has been already
      * freed, the translation below won't work, but we still want to show
      * flock owner pid number in init pidns.
      */
     if (ns == &init_pid_ns)
         return (pid_t)fl->fl_pid;
 
     rcu_read_lock();
     pid = find_pid_ns(fl->fl_pid, &init_pid_ns);
     vnr = pid_nr_ns(pid, ns);
     rcu_read_unlock();
     return vnr;
 }
 
 static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 {
     flock->l_pid = locks_translate_pid(fl, task_active_pid_ns(current));
 #if BITS_PER_LONG == 32
     /*
      * Make sure we can represent the posix lock via
      * legacy 32bit flock.
      */
     if (fl->fl_start > OFFT_OFFSET_MAX)
         return -EOVERFLOW;
     if (fl->fl_end != OFFSET_MAX && fl->fl_end > OFFT_OFFSET_MAX)
         return -EOVERFLOW;
 #endif
     flock->l_start = fl->fl_start;
     flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
         fl->fl_end - fl->fl_start + 1;
     flock->l_whence = 0;
     flock->l_type = fl->fl_type;
     return 0;
 }
 
 #if BITS_PER_LONG == 32
 static void posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)
 {
     flock->l_pid = locks_translate_pid(fl, task_active_pid_ns(current));
     flock->l_start = fl->fl_start;
     flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
         fl->fl_end - fl->fl_start + 1;
     flock->l_whence = 0;
     flock->l_type = fl->fl_type;
 }
 #endif
 
 /* Report the first existing lock that would conflict with l.
  * This implements the F_GETLK command of fcntl().
  */
 int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock *flock)
 {
     struct file_lock *fl;
     int error;
 
     fl = locks_alloc_lock();
     if (fl == NULL)
         return -ENOMEM;
     error = -EINVAL;
     if (flock->l_type != F_RDLCK && flock->l_type != F_WRLCK)
         goto out;
 
     error = flock_to_posix_lock(filp, fl, flock);
     if (error)
         goto out;
 
     if (cmd == F_OFD_GETLK) {
         error = -EINVAL;
         if (flock->l_pid != 0)
             goto out;
 
         fl->fl_flags |= FL_OFDLCK;
         fl->fl_owner = filp;
     }
 
     error = vfs_test_lock(filp, fl);
     if (error)
         goto out;
 
     flock->l_type = fl->fl_type;
     if (fl->fl_type != F_UNLCK) {
         error = posix_lock_to_flock(flock, fl);
         if (error)
             goto out;
     }
 out:
     locks_free_lock(fl);
     return error;
 }
 
 /**
  * vfs_lock_file - file byte range lock
  * @filp: The file to apply the lock to
  * @cmd: type of locking operation (F_SETLK, F_GETLK, etc.)
  * @fl: The lock to be applied
  * @conf: Place to return a copy of the conflicting lock, if found.
  *
  * A caller that doesn't care about the conflicting lock may pass NULL
  * as the final argument.
  *
  * If the filesystem defines a private ->lock() method, then @conf will
  * be left unchanged; so a caller that cares should initialize it to
  * some acceptable default.
  *
  * To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX
  * locks, the ->lock() interface may return asynchronously, before the lock has
  * been granted or denied by the underlying filesystem, if (and only if)
  * lm_grant is set. Callers expecting ->lock() to return asynchronously
  * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
  * the request is for a blocking lock. When ->lock() does return asynchronously,
  * it must return FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock
  * request completes.
  * If the request is for non-blocking lock the file system should return
  * FILE_LOCK_DEFERRED then try to get the lock and call the callback routine
  * with the result. If the request timed out the callback routine will return a
  * nonzero return code and the file system should release the lock. The file
  * system is also responsible to keep a corresponding posix lock when it
  * grants a lock so the VFS can find out which locks are locally held and do
  * the correct lock cleanup when required.
  * The underlying filesystem must not drop the kernel lock or call
  * ->lm_grant() before returning to the caller with a FILE_LOCK_DEFERRED
  * return code.
  */
 int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)
 {
     if (filp->f_op->lock)
         return filp->f_op->lock(filp, cmd, fl);
     else
         return posix_lock_file(filp, fl, conf);
 }
 EXPORT_SYMBOL_GPL(vfs_lock_file);
 
 static int do_lock_file_wait(struct file *filp, unsigned int cmd,
                  struct file_lock *fl)
 {
     int error;
 
     error = security_file_lock(filp, fl->fl_type);
     if (error)
         return error;
 
     for (;;) {
         error = vfs_lock_file(filp, cmd, fl, NULL);
         if (error != FILE_LOCK_DEFERRED)
             break;
         error = wait_event_interruptible(fl->fl_wait,
                     list_empty(&fl->fl_blocked_member));
         if (error)
             break;
     }
     locks_delete_block(fl);
 
     return error;
 }
 
 /* Ensure that fl->fl_file has compatible f_mode for F_SETLK calls */
 static int
 check_fmode_for_setlk(struct file_lock *fl)
 {
     switch (fl->fl_type) {
     case F_RDLCK:
         if (!(fl->fl_file->f_mode & FMODE_READ))
             return -EBADF;
         break;
     case F_WRLCK:
         if (!(fl->fl_file->f_mode & FMODE_WRITE))
             return -EBADF;
     }
     return 0;
 }
 
 /* Apply the lock described by l to an open file descriptor.
  * This implements both the F_SETLK and F_SETLKW commands of fcntl().
  */
 int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
         struct flock *flock)
 {
     struct file_lock *file_lock = locks_alloc_lock();
     struct inode *inode = locks_inode(filp);
     struct file *f;
     int error;
 
     if (file_lock == NULL)
         return -ENOLCK;
 
     error = flock_to_posix_lock(filp, file_lock, flock);
     if (error)
         goto out;
 
     error = check_fmode_for_setlk(file_lock);
     if (error)
         goto out;
 
     /*
      * If the cmd is requesting file-private locks, then set the
      * FL_OFDLCK flag and override the owner.
      */
     switch (cmd) {
     case F_OFD_SETLK:
         error = -EINVAL;
         if (flock->l_pid != 0)
             goto out;
 
         cmd = F_SETLK;
         file_lock->fl_flags |= FL_OFDLCK;
         file_lock->fl_owner = filp;
         break;
     case F_OFD_SETLKW:
         error = -EINVAL;
         if (flock->l_pid != 0)
             goto out;
 
         cmd = F_SETLKW;
         file_lock->fl_flags |= FL_OFDLCK;
         file_lock->fl_owner = filp;
         fallthrough;
     case F_SETLKW:
         file_lock->fl_flags |= FL_SLEEP;
     }
 
     error = do_lock_file_wait(filp, cmd, file_lock);
 
     /*
      * Attempt to detect a close/fcntl race and recover by releasing the
      * lock that was just acquired. There is no need to do that when we're
      * unlocking though, or for OFD locks.
      */
     if (!error && file_lock->fl_type != F_UNLCK &&
         !(file_lock->fl_flags & FL_OFDLCK)) {
         struct files_struct *files = current->files;
         /*
          * We need that spin_lock here - it prevents reordering between
          * update of i_flctx->flc_posix and check for it done in
          * close(). rcu_read_lock() wouldn't do.
          */
         spin_lock(&files->file_lock);
         f = files_lookup_fd_locked(files, fd);
         spin_unlock(&files->file_lock);
         if (f != filp) {
             file_lock->fl_type = F_UNLCK;
             error = do_lock_file_wait(filp, cmd, file_lock);
             WARN_ON_ONCE(error);
             error = -EBADF;
         }
     }
 out:
     trace_fcntl_setlk(inode, file_lock, error);
     locks_free_lock(file_lock);
     return error;
 }
 
 #if BITS_PER_LONG == 32
 /* Report the first existing lock that would conflict with l.
  * This implements the F_GETLK command of fcntl().
  */
 int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 *flock)
 {
     struct file_lock *fl;
     int error;
 
     fl = locks_alloc_lock();
     if (fl == NULL)
         return -ENOMEM;
 
     error = -EINVAL;
     if (flock->l_type != F_RDLCK && flock->l_type != F_WRLCK)
         goto out;
 
     error = flock64_to_posix_lock(filp, fl, flock);
     if (error)
         goto out;
 
     if (cmd == F_OFD_GETLK) {
         error = -EINVAL;
         if (flock->l_pid != 0)
             goto out;
 
         cmd = F_GETLK64;
         fl->fl_flags |= FL_OFDLCK;
         fl->fl_owner = filp;
     }
 
     error = vfs_test_lock(filp, fl);
     if (error)
         goto out;
 
     flock->l_type = fl->fl_type;
     if (fl->fl_type != F_UNLCK)
         posix_lock_to_flock64(flock, fl);
 
 out:
     locks_free_lock(fl);
     return error;
 }
 
 /* Apply the lock described by l to an open file descriptor.
  * This implements both the F_SETLK and F_SETLKW commands of fcntl().
  */
 int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
         struct flock64 *flock)
 {
     struct file_lock *file_lock = locks_alloc_lock();
     struct file *f;
     int error;
 
     if (file_lock == NULL)
         return -ENOLCK;
 
     error = flock64_to_posix_lock(filp, file_lock, flock);
     if (error)
         goto out;
 
     error = check_fmode_for_setlk(file_lock);
     if (error)
         goto out;
 
     /*
      * If the cmd is requesting file-private locks, then set the
      * FL_OFDLCK flag and override the owner.
      */
     switch (cmd) {
     case F_OFD_SETLK:
         error = -EINVAL;
         if (flock->l_pid != 0)
             goto out;
 
         cmd = F_SETLK64;
         file_lock->fl_flags |= FL_OFDLCK;
         file_lock->fl_owner = filp;
         break;
     case F_OFD_SETLKW:
         error = -EINVAL;
         if (flock->l_pid != 0)
             goto out;
 
         cmd = F_SETLKW64;
         file_lock->fl_flags |= FL_OFDLCK;
         file_lock->fl_owner = filp;
         fallthrough;
     case F_SETLKW64:
         file_lock->fl_flags |= FL_SLEEP;
     }
 
     error = do_lock_file_wait(filp, cmd, file_lock);
 
     /*
      * Attempt to detect a close/fcntl race and recover by releasing the
      * lock that was just acquired. There is no need to do that when we're
      * unlocking though, or for OFD locks.
      */
     if (!error && file_lock->fl_type != F_UNLCK &&
         !(file_lock->fl_flags & FL_OFDLCK)) {
         struct files_struct *files = current->files;
         /*
          * We need that spin_lock here - it prevents reordering between
          * update of i_flctx->flc_posix and check for it done in
          * close(). rcu_read_lock() wouldn't do.
          */
         spin_lock(&files->file_lock);
         f = files_lookup_fd_locked(files, fd);
         spin_unlock(&files->file_lock);
         if (f != filp) {
             file_lock->fl_type = F_UNLCK;
             error = do_lock_file_wait(filp, cmd, file_lock);
             WARN_ON_ONCE(error);
             error = -EBADF;
         }
     }
 out:
     locks_free_lock(file_lock);
     return error;
 }
 #endif /* BITS_PER_LONG == 32 */
 
 /*
  * This function is called when the file is being removed
  * from the task's fd array.  POSIX locks belonging to this task
  * are deleted at this time.
  */
 void locks_remove_posix(struct file *filp, fl_owner_t owner)
 {
     int error;
     struct inode *inode = locks_inode(filp);
     struct file_lock lock;
     struct file_lock_context *ctx;
 
     /*
      * If there are no locks held on this file, we don't need to call
      * posix_lock_file().  Another process could be setting a lock on this
      * file at the same time, but we wouldn't remove that lock anyway.
      */
     ctx =  smp_load_acquire(&inode->i_flctx);
     if (!ctx || list_empty(&ctx->flc_posix))
         return;
 
     locks_init_lock(&lock);
     lock.fl_type = F_UNLCK;
     lock.fl_flags = FL_POSIX | FL_CLOSE;
     lock.fl_start = 0;
     lock.fl_end = OFFSET_MAX;
     lock.fl_owner = owner;
     lock.fl_pid = current->tgid;
     lock.fl_file = filp;
     lock.fl_ops = NULL;
     lock.fl_lmops = NULL;
 
     error = vfs_lock_file(filp, F_SETLK, &lock, NULL);
 
     if (lock.fl_ops && lock.fl_ops->fl_release_private)
         lock.fl_ops->fl_release_private(&lock);
     trace_locks_remove_posix(inode, &lock, error);
 }
 EXPORT_SYMBOL(locks_remove_posix);
 
 /* The i_flctx must be valid when calling into here */
 static void
 locks_remove_flock(struct file *filp, struct file_lock_context *flctx)
 {
     struct file_lock fl;
     struct inode *inode = locks_inode(filp);
 
     if (list_empty(&flctx->flc_flock))
         return;
 
     flock_make_lock(filp, &fl, F_UNLCK);
     fl.fl_flags |= FL_CLOSE;
 
     if (filp->f_op->flock)
         filp->f_op->flock(filp, F_SETLKW, &fl);
     else
         flock_lock_inode(inode, &fl);
 
     if (fl.fl_ops && fl.fl_ops->fl_release_private)
         fl.fl_ops->fl_release_private(&fl);
 }
 
 /* The i_flctx must be valid when calling into here */
 static void
 locks_remove_lease(struct file *filp, struct file_lock_context *ctx)
 {
     struct file_lock *fl, *tmp;
     LIST_HEAD(dispose);
 
     if (list_empty(&ctx->flc_lease))
         return;
 
     percpu_down_read(&file_rwsem);
     spin_lock(&ctx->flc_lock);
     list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list)
         if (filp == fl->fl_file)
             lease_modify(fl, F_UNLCK, &dispose);
     spin_unlock(&ctx->flc_lock);
     percpu_up_read(&file_rwsem);
 
     locks_dispose_list(&dispose);
 }
 
 /*
  * This function is called on the last close of an open file.
  */
 void locks_remove_file(struct file *filp)
 {
     struct file_lock_context *ctx;
 
     ctx = smp_load_acquire(&locks_inode(filp)->i_flctx);
     if (!ctx)
         return;
 
     /* remove any OFD locks */
     locks_remove_posix(filp, filp);
 
     /* remove flock locks */
     locks_remove_flock(filp, ctx);
 
     /* remove any leases */
     locks_remove_lease(filp, ctx);
 
     spin_lock(&ctx->flc_lock);
     locks_check_ctx_file_list(filp, &ctx->flc_posix, "POSIX");
     locks_check_ctx_file_list(filp, &ctx->flc_flock, "FLOCK");
     locks_check_ctx_file_list(filp, &ctx->flc_lease, "LEASE");
     spin_unlock(&ctx->flc_lock);
 }
 
 /**
  * vfs_cancel_lock - file byte range unblock lock
  * @filp: The file to apply the unblock to
  * @fl: The lock to be unblocked
  *
  * Used by lock managers to cancel blocked requests
  */
 int vfs_cancel_lock(struct file *filp, struct file_lock *fl)
 {
     if (filp->f_op->lock)
         return filp->f_op->lock(filp, F_CANCELLK, fl);
     return 0;
 }
 EXPORT_SYMBOL_GPL(vfs_cancel_lock);
 
 #ifdef CONFIG_PROC_FS
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 
 struct locks_iterator {
     int li_cpu;
     loff_t  li_pos;
 };
 
 static void lock_get_status(struct seq_file *f, struct file_lock *fl,
                 loff_t id, char *pfx, int repeat)
 {
     struct inode *inode = NULL;
     unsigned int fl_pid;
     struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
     int type;
 
     fl_pid = locks_translate_pid(fl, proc_pidns);
     /*
      * If lock owner is dead (and pid is freed) or not visible in current
      * pidns, zero is shown as a pid value. Check lock info from
      * init_pid_ns to get saved lock pid value.
      */
 
     if (fl->fl_file != NULL)
         inode = locks_inode(fl->fl_file);
 
     seq_printf(f, "%lld: ", id);
 
     if (repeat)
         seq_printf(f, "%*s", repeat - 1 + (int)strlen(pfx), pfx);
 
     if (IS_POSIX(fl)) {
         if (fl->fl_flags & FL_ACCESS)
             seq_puts(f, "ACCESS");
         else if (IS_OFDLCK(fl))
             seq_puts(f, "OFDLCK");
         else
             seq_puts(f, "POSIX ");
 
         seq_printf(f, " %s ",
                  (inode == NULL) ? "*NOINODE*" : "ADVISORY ");
     } else if (IS_FLOCK(fl)) {
         seq_puts(f, "FLOCK  ADVISORY  ");
     } else if (IS_LEASE(fl)) {
         if (fl->fl_flags & FL_DELEG)
             seq_puts(f, "DELEG  ");
         else
             seq_puts(f, "LEASE  ");
 
         if (lease_breaking(fl))
             seq_puts(f, "BREAKING  ");
         else if (fl->fl_file)
             seq_puts(f, "ACTIVE    ");
         else
             seq_puts(f, "BREAKER   ");
     } else {
         seq_puts(f, "UNKNOWN UNKNOWN  ");
     }
     type = IS_LEASE(fl) ? target_leasetype(fl) : fl->fl_type;
 
     seq_printf(f, "%s ", (type == F_WRLCK) ? "WRITE" :
                  (type == F_RDLCK) ? "READ" : "UNLCK");
     if (inode) {
         /* userspace relies on this representation of dev_t */
         seq_printf(f, "%d %02x:%02x:%lu ", fl_pid,
                 MAJOR(inode->i_sb->s_dev),
                 MINOR(inode->i_sb->s_dev), inode->i_ino);
     } else {
         seq_printf(f, "%d <none>:0 ", fl_pid);
     }
     if (IS_POSIX(fl)) {
         if (fl->fl_end == OFFSET_MAX)
             seq_printf(f, "%Ld EOF\n", fl->fl_start);
         else
             seq_printf(f, "%Ld %Ld\n", fl->fl_start, fl->fl_end);
     } else {
         seq_puts(f, "0 EOF\n");
     }
 }
 
 static struct file_lock *get_next_blocked_member(struct file_lock *node)
 {
     struct file_lock *tmp;
 
     /* NULL node or root node */
     if (node == NULL || node->fl_blocker == NULL)
         return NULL;
 
     /* Next member in the linked list could be itself */
     tmp = list_next_entry(node, fl_blocked_member);
     if (list_entry_is_head(tmp, &node->fl_blocker->fl_blocked_requests, fl_blocked_member)
         || tmp == node) {
         return NULL;
     }
 
     return tmp;
 }
 
 static int locks_show(struct seq_file *f, void *v)
 {
     struct locks_iterator *iter = f->private;
     struct file_lock *cur, *tmp;
     struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
     int level = 0;
 
     cur = hlist_entry(v, struct file_lock, fl_link);
 
     if (locks_translate_pid(cur, proc_pidns) == 0)
         return 0;
 
     /* View this crossed linked list as a binary tree, the first member of fl_blocked_requests
      * is the left child of current node, the next silibing in fl_blocked_member is the
      * right child, we can alse get the parent of current node from fl_blocker, so this
      * question becomes traversal of a binary tree
      */
     while (cur != NULL) {
         if (level)
             lock_get_status(f, cur, iter->li_pos, "-> ", level);
         else
             lock_get_status(f, cur, iter->li_pos, "", level);
 
         if (!list_empty(&cur->fl_blocked_requests)) {
             /* Turn left */
             cur = list_first_entry_or_null(&cur->fl_blocked_requests,
                 struct file_lock, fl_blocked_member);
             level++;
         } else {
             /* Turn right */
             tmp = get_next_blocked_member(cur);
             /* Fall back to parent node */
             while (tmp == NULL && cur->fl_blocker != NULL) {
                 cur = cur->fl_blocker;
                 level--;
                 tmp = get_next_blocked_member(cur);
             }
             cur = tmp;
         }
     }
 
     return 0;
 }
 
 static void __show_fd_locks(struct seq_file *f,
             struct list_head *head, int *id,
             struct file *filp, struct files_struct *files)
 {
     struct file_lock *fl;
 
     list_for_each_entry(fl, head, fl_list) {
 
         if (filp != fl->fl_file)
             continue;
         if (fl->fl_owner != files &&
             fl->fl_owner != filp)
             continue;
 
         (*id)++;
         seq_puts(f, "lock:\t");
         lock_get_status(f, fl, *id, "", 0);
     }
 }
 
 void show_fd_locks(struct seq_file *f,
           struct file *filp, struct files_struct *files)
 {
     struct inode *inode = locks_inode(filp);
     struct file_lock_context *ctx;
     int id = 0;
 
     ctx = smp_load_acquire(&inode->i_flctx);
     if (!ctx)
         return;
 
     spin_lock(&ctx->flc_lock);
     __show_fd_locks(f, &ctx->flc_flock, &id, filp, files);
     __show_fd_locks(f, &ctx->flc_posix, &id, filp, files);
     __show_fd_locks(f, &ctx->flc_lease, &id, filp, files);
     spin_unlock(&ctx->flc_lock);
 }
 
 static void *locks_start(struct seq_file *f, loff_t *pos)
     __acquires(&blocked_lock_lock)
 {
     struct locks_iterator *iter = f->private;
 
     iter->li_pos = *pos + 1;
     percpu_down_write(&file_rwsem);
     spin_lock(&blocked_lock_lock);
     return seq_hlist_start_percpu(&file_lock_list.hlist, &iter->li_cpu, *pos);
 }
 
 static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
 {
     struct locks_iterator *iter = f->private;
 
     ++iter->li_pos;
     return seq_hlist_next_percpu(v, &file_lock_list.hlist, &iter->li_cpu, pos);
 }
 
 static void locks_stop(struct seq_file *f, void *v)
     __releases(&blocked_lock_lock)
 {
     spin_unlock(&blocked_lock_lock);
     percpu_up_write(&file_rwsem);
 }
 
 static const struct seq_operations locks_seq_operations = {
     .start  = locks_start,
     .next   = locks_next,
     .stop   = locks_stop,
     .show   = locks_show,
 };
 
 static int __init proc_locks_init(void)
 {
     proc_create_seq_private("locks", 0, NULL, &locks_seq_operations,
             sizeof(struct locks_iterator), NULL);
     return 0;
 }
 fs_initcall(proc_locks_init);
 #endif
 
 static int __init filelock_init(void)
 {
     int i;
 
     flctx_cache = kmem_cache_create("file_lock_ctx",
             sizeof(struct file_lock_context), 0, SLAB_PANIC, NULL);
 
     filelock_cache = kmem_cache_create("file_lock_cache",
             sizeof(struct file_lock), 0, SLAB_PANIC, NULL);
 
     for_each_possible_cpu(i) {
         struct file_lock_list_struct *fll = per_cpu_ptr(&file_lock_list, i);
 
         spin_lock_init(&fll->lock);
         INIT_HLIST_HEAD(&fll->hlist);
     }
 
     lease_notifier_chain_init();
     return 0;
 }
 core_initcall(filelock_init);